A conventional heat exchanger for cooling intake air pressurized by a supercharger before introduced into an internal combustion engine has a core portion having a plurality of tubes and serving as a heat exchanging portion and a header tank communicated with the plurality of tubes in the core portion.
FIG. 8 depicts a sectional view of an example of a structure of the above header tank. A core plate 911 to which a tube 922 is blazed and a tank body 912 are joined to each other to form the header tank 910 and a chamber 910a therein. Two side walls 912b at both sides of the tank body 912 are supported by a support bar 912a disposed therebetween and joined thereto such by welding, in a manner of penetrating the chamber 910a. 
Recent emission regulation requires to increase boost pressure. If the header tank 910 does not have the support bar 912a, the boost pressure may deform the tank body 912 to bulge outward, and also deform the core plate 911 to increase a distance between edges 911b thereof. This deformation generates a large stress at a connection 911a of the core plate 911 and the tube 922 inducing defect such as a fracture at the connection. The support bar 912a is for preventing the above defect.
However, the above conventional heat exchanger requires to bore the tank body 912 for fixing the support bar 912a and to weld the support bar 912a to the tank body 912 in a manner of securing the airtightness. The structure of the above heat exchanger makes the manufacture complex and increases manufacturing facilities and the manufacturing processes of the heat exchanger.
The inventors of the present invention has focused attention on stress reduction generating at the connection of the core plate and the tube, and discovered a heat exchanger capable of reducing the stress at the connection without the support bar and just by limiting deformation of only the core plate.